1. Field of the Invention
This invention relates to the field of headwear. More specifically, the invention comprises a baseball cap having a modified bill configured to produce downforce when the cap is placed in a moving airstream.
2. Description of the Related Art
The “baseball cap” is one of the world's best known hats. FIG. 1 shows a typical example. Baseball cap 10 is comprised of head covering 12 and bill 14. Head covering 12 is a generally circular assembly of flexible material sized to fit fairly closely over the human head. Bill 14 has leading edge 52 and trailing edge 54. The trailing edge is attached to the forward portion of the head covering. As the hat is normally worn, the bill extends forward from the wearer's face. The bill provides shade and weather protection for the user's face.
Those familiar with the art will know that such hats are made using a variety of technique. The example of FIG. 1 is constructed using a sewn assembly of wedge-shaped pieces. These are curved inward and join at the top, where a button is usually affixed. Such hats must typically include size-adjusting features. The rear of the hat may have a break spanned by an adjustable strap. The strap is used to adjust the circumference of the hat at its largest section. Alternatively, the head covering may include elastic material which eliminates the need for other adjustment features.
FIG. 2 shows an elevation view of a person actually wearing a prior art baseball cap. Such caps are often worn while traveling in an open vehicle—such as a fishing boat. Air flow directed toward the wearer's face has a tendency to lift the baseball cap off the wearer's head. As for most situations involving subsonic compressible flow, the phenomenon is explained by the application of Bernoulli's equation, which can be written as:
                    1        2            ⁢              v        1        2              +          gh      1        +                  P        1                    ρ        1              =                    1        2            ⁢              v        2        2              +          gh      2        +                  P        2                    ρ        2            In this expression, v stands for the flow velocity at a given point, g stands for gravitational acceleration, h stands for the height above a reference plane, P stands for the pressure of the air at a given point, and ρ stands for the density of the air at a given point.
From this equation one may easily discern the fact that when a compressible fluid is flowing past an object at subsonic speeds, the faster the flow is sin a particular region the lower the pressure will be in that region. When looking at FIG. 2, the reader will observe how the flow must split to flow over the top and bottom of bill 14. The flow over the top passes smoothly over the head covering and is not decelerated very much. This is denoted in the view as high velocity region 18.
The flow passing under the bill, however, impacts the wearer's face 16. This produces a recirculation area denoted as stagnation region 20. The flow in this area is relatively slow. Thus, from Bernoulli's equation, one may accurately predict that the air pressure in the area beneath the bill will be greater than the air pressure in the area above the bill. The result is the creation of lift 24, which tends to lift the cap free of the wearer's head.
Prior hat designers have accounted for this phenomenon by angling the bill downward as shown. The downward angle has the effect of an airfoil having a negative angle of attack. The flow over the top therefore creates downforce 22. If the magnitude of downforce 22 exceeds that of lift 24, then the hat will stay on. Of course, the motion of the wearer's head alters the bill's angle of attack. If the user inclines her head slightly, downforce 22 will be greatly reduced. This will likely be the instant when the moving airstream lifts the cap free of the wearer's head and carries it away.
The loss of such a cap is a significant inconvenience. This is particularly true in a boating situation, where the hat is likely to blow overboard and be lost. Prior art designers have attempted to remedy this known problem in a variety of ways. For example, some caps have incorporated a bill having a hinged vent flap. The vent flap pivots upward if the pressure difference between the region beneath the bill and above the bill becomes large enough. Other designs have incorporated one or more fixed vents through the bill. Still other designs have incorporated a bill with a severe downward angle, so that the bill's angle of attack remains negative throughout the range of motion of the user's head.
While these prior art designs have in part remedied the problem, no prior art design has produced a good solution while still maintaining the conventional benefits of the traditional baseball cap. The present invention seeks to remedy these shortcomings.